Bendii Syndrome is a neurological condition which affects a minority of elderly Vulcans, similar to Alzheimer's disease in human beings. The disease's symptoms include wasting, weakness, fatigue, fever, and a gradual but accelerating loss of emotional control, with victims exhibiting sudden bursts of emotion. A diagnosis can be made by culturing tissue samples from the affected person's metathalamus.
The most dangerous side effect of Bendii is that an affected person's loss of emotional control can be telepathically transmitted to others in the person's vicinity. Ordinarily, an attending Vulcan healer can suppress these effects, but if the telepath him/herself is stressed, this effect can still persist.
In the alternate reality caused by the Romulan known as Nero, Starfleet Ensign Kelsi Nielsen assisted the Spock from the prime timeline (a/k/a Spock Prime) in developing a medicine that has shown great promise in either slowing or altogether stopping the onset of Bendii's. (A Flight to Remember)